Theoretical insights into the effects of RE doping on the structural, electronic, and optical properties of magnesium clusters

Doping of magnesium-based materials with the rare earth (RE) elements allows one to adjust or modify the structures and properties of the materials. In the present work, the structural, electronic, and optical properties of the global minima Mg-n (n = 2-10) and MgnX (X = Sc, Y, La, Nd, Gd, n = 1-9) clusters have been examined using the density functional theory (DFT) and the time-dependent DFT. The identified structures show that the RE atoms tend to occupy the center of the surface of the geometries, which enhances their structural stability. Further analyses on average bonding energies, the second-order differences in energy, and HOMO-LUMO gaps indicate that the Mg3Nd cluster is more stable than others. The excellent stability of this cluster is caused by the strong Nd 4f and Mg 2p interactions through the analyses of molecular orbitals. The natural population analyses imply that the electron transfers mainly occur among the s-p-d orbitals in MgnX (X = Sc, Y, La) clusters and the s-d-f orbitals in MgnX (X = Nd, Gd). In addition, the results of the excited-state calculations reveal that the absorption spectra of all MgnX clusters emerge red-shift phenomena compared with that of Mg-n, and the absorbance strongest resonances of Mg4X clusters concentrate at visible light region (about 600 nm).